Wastewater treatment is the process of removing targeted contaminants from a wastewater stream. Wastewater treatment typically involves a series of treatment steps including chemical, biological and physical treatment measures to remove the targeted contaminants. A typical wastewater treatment facility includes a number of physical components that operate in series to remove the targeted contaminants. The treatment components used in a wastewater treatment facility will differ depending upon the targeted contaminants to be removed.
One common step in wastewater treatment includes a sedimentation stage where the wastewater stream is allowed to slowly pass through a large tank, referred to as clarifier or sedimentation tank. The primary purpose of a clarifier is to remove solids that may be found in the wastewater stream, thus producing a homogenous liquid that is capable of being treated biologically and/or chemically in final treatment steps.
One of the final stages in a wastewater treatment facility for treating water that is to be released to the environment, or in a water purification system where drinking water is to be produced, is the use of a reverse osmosis (RO) unit and/or an ultra-filtration unit. Ultra-filtration defines a number of different membrane filtration systems in which hydrostatic pressure forces a liquid against one or more semi-permeable membranes. Suspended solids and solutes are retained in the filter, while water and lower molecular weight solutes are passed through the membranes and are recovered as the desired end product. In some processes, ultra-filtration may be a pre-treatment step for a final treatment step using reverse osmosis. As understood by those skilled in the art, a reverse osmosis process is a separation or filtration method that utilizes hydrostatic pressure to force the stream of liquid through a membrane that retains the solute on one side, and allows the pure solvent to pass on the other side of the membrane. Reverse osmosis may alternatively be defined as a process of forcing a solvent from an area of high solute concentration through a membrane to a region of lower solute concentration by application of a pressure in excess of the osmotic pressure.
One particular limitation in the use of a reverse osmosis unit, as well as ultra-filtration units, is that the membranes will become clogged over time, and some reverse flow is required to cause a loosening of the material collected on the membrane surfaces. This reverse flow or backwash requires a temporary shut-down of the waste treatment process. The backwash requirement slows the processing capability of the treatment system.
An ultra-filtration unit typically includes a plurality of separate filter elements that are placed within a tank, and a flow of liquid is provided to the tank in which water is drawn through the filters thereby creating a filtered stream of liquid. Upstream of the ultra-filtration unit may be one or more additional treatment units, such as a clarifier that removes a certain percentage of solids from the liquid stream prior to reaching the ultra-filtration unit. Because the liquid stream is typically carried by a pipe, the remaining solids within the liquid stream reaching the tank holding the ultra-filtration filters is well mixed due to the natural mixing action that occurs within a pipe that may travel a considerable distance and have multiple bends or turns. Therefore, the loading on the ultra-filtration filters comprises most if not all of the solid material that is carried in the liquid stream at that stage.
As a backwash operation is conducted, solid material is loosened from the surfaces of the membranes, and the tank holding the ultra-filtration filters must be drained/cleaned to remove the solids that collect on the bottom surface of the tank. This cleaning requirement further delays the operation of the waste treatment facility.
Therefore, there is a need to provide a waste treatment system and method in which solids introduced to an ultra-filtration unit are minimized to thereby increase the overall efficiency of the ultra-filtration units, which in turn, will reduce the frequency of required backwash and will therefore increase overall system efficiency.
Additionally, there is also a need to reduce the amount of equipment required to accommodate an ultra-filtration unit that not only minimizes the amount of materials used, but also the required space for ultra-filtration.
There is also a need to provide an ultra-filtration unit that minimizes operational and maintenance cost for backwashing the filtration system, yet still provides easy access to the working components of the filtration system.